Polishing pad, composition for the manufacture thereof, and method of making and using

ABSTRACT

A polyurethane layer for forming a polishing pad for a semiconductor wafer is described, wherein the polyurethane layer comprises: a foamed polyurethane, wherein the polyurethane foam has a density of about 640 to about 960 kg/m 3 , and a plurality of cells having an average diameter of about 20 to about 200 micrometers; and particles of a hydrophobic polymer having a critical surface energy of less than 35 mN/m and having a median particle size of 3 to 100 micrometers. Polishing pads as well as methods for polishing are also described.

CROSS REFERENCE TO RELATED APPLICATION

This application is a US. Non-Provisional application of, and claims thebenefit of, U.S. Provisional Application Ser. No. 61/181,398, filed onMay 27, 2009, which is incorporated herein by reference in its entirety.

BACKGROUND

This application relates to articles and methods for chemical-mechanicalpolishing. In particular, the invention relates to a chemical-mechanicalpolishing pad for precisely and rapidly polishing a surface of asemiconductor wafer or the like.

In recent years, chemical-mechanical polishing (CMP) has become thetechnology of choice among semiconductor chip fabricators to planarizethe surface of semiconductor chips as circuit pattern layers are laiddown. CMP technology is well known, and is typically accomplished usinga polishing pad and a polishing composition.

The fabrication of semiconductor wafers typically involves the formationof a plurality of integrated circuits on a semiconductor substrate of,for example, silicon, gallium arsenide, indium phosphide, or the like.The integrated circuits are generally formed by a series of processsteps in which patterned layers of materials, such as conductive,insulating, and semiconducting materials, are formed on the substrate.In order to maximize the density of integrated circuits per wafer, anextremely planar, precision-polished substrate is needed at variousstages throughout the semiconductor wafer production process. As such,semiconductor wafer production typically involves the use of at leastone, and more typically more than one polishing step.

The polishing steps typically involve rotating or rubbing a polishingpad and semiconductor wafer substrate against each other in the presenceof a polishing fluid or composition, usually using a controlled andrepetitive motion. The pad aids in mechanical polishing of thesemiconductor substrate, while the polishing fluid aids in bothmechanical and chemical polishing of the substrate and facilitates theremoval and transport of abraded material off of and away from the roughsurface of the article. Typically, a polishing fluid is interposedbetween the rough surface of the article that is to be polished and thework surface of the polishing pad. The polishing fluid is often alkalineand may contain an abrasive material, e.g., particulate cerium oxide orsilica, among others. Polishing can be used to remove either metals,dielectrics, or other materials in the electronics industry.

Various CMP pads of different materials have been described or are incurrent use, for example a metal pad described in U.S. Pat. No.6,022,268; a polishing pad containing particles as described in U.S.Pat. No. 5,489,233; a polishing pad of polymer-impregnated woven fibersold under the trade name POLITEX; and a pad of a polymer sheetcontaining void spaces formed by in situ production or incorporation ofhollow fill materials (sold under the trademark IC 1000). A compositepad of multiple layers of materials having an outer substrate thatcontacts the surface of the semiconductor being polished is includedamong pads in current use. CMP pads made from porous foamed materialsare also known. For example, U.S. Pat. No. 6,913,517 describes amicroporous polyurethane polishing pad, and U.S. Pat. No. 4,954,141describes polishing pads made of a foamed fluorine-containing polymer.U.S. Pat. No. 7,059,936 describes a polishing pad having a low surfaceenergy, particularly for use with a hydrophobic polishing composition.

Despite intensive development directed to CMP pads, there remains acontinuing perceived need in the art for continual improvement ofpolishing efficiency and effectiveness, in particular characterized bylow defects. With CMP pads, there is often a trade-off between rate ofremoval, when polishing material away, and defect level in the polishedwafer. In other words, a harder pad can result in faster polishing,which in turn can result in higher defects. It would be desirable toobtain a CMP pad that polishes fast, is highly efficient, and yetresults in a low defect level.

Further, when using a highly active polishing composition for polishinga semiconductor wafer, the chemical properties and mechanical structureof the CMP pad can deteriorate. As a result, the efficiency of thepolishing pad can decrease, for example, the polishing rate can bereduced, and increased surface roughness, undulations, and/or damage canresult. Frequent replacement of an expensive polishing pad by a costlynew pad is undesirable. Furthermore, even when a pad deteriorates onlyslightly over time, the conditions of polishing such as workingpressure, rotation speed of a polishing plate, and temperature and flowrate of cooling water for the polishing plate can require continuouscontrol to cope with the degree of deterioration, in order to obtain thedesired polishing of a surface of a semiconductor wafer. It would bedesirable to obtain a CMP pad that has improved resistance todeterioration after repeated polishing of wafers.

Thus, there remains a continuing need in the art for improved CMP pads,particularly pads that provide polished surfaces with low defects. Itwould be a further advantage for such pads to have good resistance todeterioration, as well as good polishing efficiency, workability, andlow cost. It would still further be desirable to more finely control ortailor the abrasive properties of the polishing pad to balance itsability to remove a particular coating without attacking a particularsurface material or cause unwanted scratching or other damage. It wouldalso be desirable to be able to economically manufacture and customizesuch pads for a particular application.

SUMMARY

In order to overcome the problems described above and to accomplish thedesired objects, a polyurethane layer comprises: a foamed polyurethane,wherein the polyurethane foam has a density of about 640 to about 1200kg/m³, a plurality of cells having an average diameter of about 20 toabout 200 micrometers, and particles of a hydrophobic polymer having acritical surface energy of less than 35 mN/m and a median particle sizeof 3 to 100 micrometers. In one embodiment, the layer has a density ofabout 640 to 960 kg/m³.

In another embodiment, a polyurethane layer for forming a polishing padfor a semiconductor wafer comprises a polyurethane foam having

-   -   a density of about 640 to about 1200 kg/m³, and    -   a plurality of cells having an average diameter of 20 to 200        micrometers, wherein        the polyurethane layer has:    -   a KEL of about 1 to about 500 1/Pa at 50° C.,    -   a storage modulus of greater than about 100 MPa in the range of        20° C. to 50° C.,    -   a tan δ of less than about 0.070 in the range of 20° C. to 50°        C.,    -   and a ratio of tan δ at 50° C.:tan δ at 20° C. of 1.2 to 3.0.

In still another embodiment, a polyurethane layer for forming apolishing pad for a semiconductor wafer comprises a polyurethane foam,wherein the polyurethane foam has

a density of about 640 to about 1200 kg/m³, and

a tan δ of less than 0.070 in the range of 20° C. to 50° C.,

and a ratio of tan δ at 50° C.:tan δ at 20° C. of 1.2 to 3.0.

In another embodiment, a polishing pad comprises any of the abovepolyurethane layers.

A method of manufacture of a polishing pad comprises polishing a siliconwafer, comprising applying a particulate media against a surface of thesilicon wafer, and rotating a polishing pad relative to said surface,wherein the polishing pad comprises a polishing layer comprising theabove polyurethane foam.

The above described and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is scanning electron microscopic image of a comparative porouspolyurethane material; and

FIG. 2 is scanning electron microscopic image of a porous polyurethanehaving the same composition as the material of FIG. 1, except with theaddition of hydrophobic particles.

FIG. 3 is a graph showing tan delta measured over the temperature rangefrom 20 to 50° C. for one embodiment of the invention.

DETAILED DESCRIPTION

An improved polishing pad comprises a mechanically frothed polyurethanefoam formed from a specific combination of an isocyanate prepolymer,hydroxy-containing compounds, and a silicone surfactant, and comprisingparticles of a hydrophobic polymer, which results in finer cell size.Such polishing pads have a high polishing rate and provide polishedsurfaces with very low defects, even at the 0.20 micrometer detectionlevel. Less heat build-up is observed during polishing, which canpotentially provide a more stable performance with time. Thus, thepolishing pads can also have excellent resistance to deterioration evenafter prolonged use.

The polishing pads comprise a matrix of a mechanically frothedpolyurethane foam and a plurality of particles of hydrophobicparticulates, for example, particles of a hydrophobic polymer. As usedherein, the term “hydrophobic particulates” means particulates that havea low surface energy, for example, a critical surface tension of lessthan 40 mN/m, specifically less than 35 mN/m, more specifically not morethan 30 mN/m, for example 15 to 25 mN/m. Preferably, therefore, when apolymer is used in the hydrophobic particulates, the polymer containsonly a small number, if any, of hydrophilic functional or ionic groupsand, more preferably, is free of hydrophilic or ionic groups.

The hydrophobic polymer is not particularly limited and can comprise, orconsist essentially of, fluorocarbon, fluorochlorocarbon, a siloxane(e.g., an —R₂SiO— unit, where R is independently a hydrogen atom or ahydrocarbon group), or C₂₋₈ hydrocarbon repeat units, e.g., ethylene,propylene, butylene, or styrene, or a combination of the foregoingrepeat units. Thus, for example, the hydrophobic polymer can includesilicone rubber, polydiorganosiloxane (such as polydimethylsiloxane),polybutadiene, polyethylene, polypropylene, polystyrene, andpolyacrylamide.

In one specific embodiment, the hydrophobic polymer is a fluorinatedpolymer, also known as a fluoropolymer. “Fluoropolymers” as used hereininclude homopolymers and copolymers that comprise repeat units derivedfrom a fluorinated alpha-olefin monomer, i.e., an alpha-olefin monomerthat includes at least one fluorine atom substituent, and optionally, anon-fluorinated, ethylenically unsaturated monomer reactive with thefluorinated alpha-olefin monomer. Exemplary alpha-olefin monomersinclude CF₂═CF₂, CHF═CF₂, CH₂═CF₂, CH═CHF, CClF═CF₂, CCl₂═CF₂,CClF═CClF, CHF═CCl₂, CH₂═CClF, and CCl₂═CClF, CF₃CF═CF₂, CF₃CF═CHF,CF₃CH═CF₂, CF₃CH═CH₂, CF₃CF═CHF, CHF₂CH═CHF, and CF₃CH═CH₂, andperfluoro(C₂₋₈)alkylvinylethers such as perfluorooctylvinyl ether.Specifically, the fluorinated alpha-olefin monomer is one or more oftetrafluoroethylene (CF₂═CF₂), chlorotrifluoroethylene (CClF═CF₂),vinylidene fluoride (CH₂═CF₂) and hexafluoropropylene (CF₂═CFCF₃).Exemplary non-fluorinated monoethylenically unsaturated monomers includeethylene, propylene, butene, and ethylenically unsaturated aromaticmonomers such as styrene. Exemplary fluoropolymers includepoly(tetrafluoroethylene) homopolymer (PTFE), poly(hexafluoroethylene),poly(tetrafluoroethylene-hexafluoroethylene), andpoly(tetrafluoroethylene-ethylene-propylene). A specific exemplaryfluoropolymer is PTFE, which can be fibril forming or non-fibrilforming.

The particles can be about 3 to about 100 micrometers, specificallyabout 5 to about 50 micrometers. In one embodiment, particles are about3 to about 30 micrometers in median diameter, specifically about 25micrometers, which have been shown to produce a polyurethane foam havingan average cell size of about 20 to about 200 micrometers, specificallyabout 50 to about 100 micrometers, as determined by SEM (scanningelectron microscopy). Fluoropolymer particles of that size, for example,are commercially available from a variety of sources. Bimodal, trimodal,and higher modals, of different particle sizes, can be used.

Fluoropolymers can be a fine powder, dispersion, or granular form,including a coagulated dispersion made by coagulation and drying ofdispersion-manufactured PTFE. Granular PTFE (polytetrafluoroethylene),FEP (fluorinated ethylene propylene), or PFA (perfluoroalkoxy) made bysuspension polymerization can have a median particle size of about 30 toabout 40 micrometers for one standard product. The granularfluoropolymers can be cryogenically ground to exhibit a median particlesize of less than about 100 micrometers.

When present, the effective particulate fluoropolymer content of thepolyurethane-forming composition can be readily determined by one ofordinary skill in the art, depending upon the desired properties of thepolishing pad, and the polyurethane formulation. In general, effectivequantities are about 0.1 to about 5 weight percent (wt. %) of the totalpolyurethane forming composition, specifically about 1 to about 4 wt. %,and most specifically about 2 to about 3 wt. % of the total polyurethaneforming composition.

Without wishing to be bound by theory, it is believed that incorporationof hydrophobic particles into the polyurethane-forming compositionincreases the mix viscosity and provides a very fine microcellularstructure in the polyurethane. Typically, a very fine cell structure isused to create tiny surface asperities that can hold the abrasiveparticles of a polishing composition or slurry. Without being bound bytheory, it is believed that the presence of the hydrophobic particlesincreases the stability of small cells in the mechanical frothingprocess by reducing the surface energy. This results in the presence ofa larger quantity of small cells in the polishing pad. It wasunexpectedly found that, as a result, certain of the performanceproperties of the polishing pad were significantly improved, asdescribed in the Examples below, including high polishing efficiency,low polishing temperature, and low level of defects.

In addition, without wishing to be bound by theory, the surface energyof the hydrophobic particles in the polyurethane matrix may disrupt the“wetting out” of the slurry during polishing. Furthermore, it isbelieved that the presence of the hydrophobic particles in thepolyurethane causes slurry particulates, during polishing, to be heldlonger or trapped in the non-hydrophobic portions of the surface of thepolishing pad. It is believed that such phenomena, among others, canaccount for the polishing pad providing an improved amount of polishwithout causing defects. The lower surface energy of the hydrophobicparticles may also result in less friction during polishing, leading tolower polishing temperatures.

The mechanically frothed polyurethane foam matrix is formed from areactive composition comprising an organic polyisocyanate componentreactive with an active hydrogen-containing component, a foamstabilizing surfactant, and a catalyst. Organic polyisocyanates are ofthe general formula Q(NCO)_(i), wherein i is an integer having anaverage value of greater than two, and Q is a polyurethane radicalhaving a valence of i. Q(NCO)_(i) is therefore a compositionconventionally known as a prepolymer. Such prepolymers are formed byreacting a stoichiometric excess of a polyisocyanate as described abovewith an active hydrogen-containing component, for example thepolyhydroxyl-containing materials or polyols described below. In oneembodiment, the polyisocyanate is used in proportions of about 30percent to about 200 percent stoichiometric excess, the stoichiometrybeing based upon equivalents of isocyanate group per equivalent ofhydroxyl in the polyol. In a specific embodiment, a compositioncomprising an isocyanate prepolymer is mechanically frothed to obtain afoamed polyurethane material that forms a desirably firm pad. The amountof polyisocyanate used will vary slightly depending upon the nature ofthe polyurethane being prepared.

The amount of polyisocyanate used in the polyurethane-formingcomposition will vary depending upon the nature of the polyurethanebeing prepared. In general, the total —NCO equivalents to total activehydrogen equivalents is such as to provide a ratio of 0.8 to 1.2equivalents of —NCO per equivalent of active hydrogen, e.g., hydroxylhydrogen, of the active hydrogen reactant, and preferably a ratio ofabout 1.0 to 1.05 equivalents of —NCO per active hydrogen.

The active hydrogen-containing component can comprise a mixture ofdifferent types of active hydrogen-containing components, includingtriols, diols, and compounds having an average hydroxyl functionality ofgreater than 3.

In particular, the active hydrogen-containing component comprisespolyester polyols and/or polyether polyols. Suitable polyester polyolsare inclusive of polycondensation products of polyols with dicarboxylicacids or ester-forming derivatives thereof (such as anhydrides, estersand halides), polylactone polyols obtainable by ring-openingpolymerization of lactones in the presence of polyols, polycarbonatepolyols obtainable by reaction of carbonate diesters with polyols, andcastor oil polyols. Suitable dicarboxylic acids and derivatives ofdicarboxylic acids which are useful for producing polycondensationpolyester polyols are aliphatic or cycloaliphatic dicarboxylic acidssuch as glutaric, adipic, sebacic, fumaric, and maleic acids; dimericacids; aromatic dicarboxylic acids such as phthalic, isophthalic, andterephthalic acids; tribasic or higher functional polycarboxylic acidssuch as pyromellitic acid; as well as anhydrides and second alkyl esterssuch as maleic anhydride, phthalic anhydride, and dimethylterephthalate. The polymers of cyclic esters can also be used. Thepreparation of cyclic ester polymers from at least one cyclic estermonomer is exemplified by U.S. Pat. Nos. 3,021,309 through 3,021,317;3,169,945; and 2,962,524. Suitable cyclic ester monomers include but arenot limited to δ-valerolactone; ε-caprolactone; zeta-enantholactone; themonoalkyl-valerolactones, e.g., the monomethyl-, monoethyl-, andmonohexyl-valerolactones. In general the polyester polyol may comprisecaprolactone based polyester polyols, aromatic polyester polyols,ethylene glycol adipate based polyols, and mixtures comprising any oneof the foregoing polyester polyols. Polyester polyols made fromε-caprolactones, adipic acid, phthalic anhydride, and terephthalic acidor dimethyl esters of terephthalic acid are generally preferred.

Polyether polyols can be obtained by the chemical addition of alkyleneoxides, such as ethylene oxide, propylene oxide and mixtures thereof, towater or polyhydric organic components, such as ethylene glycol,propylene glycol, trimethylene glycol, 1,2-butylene glycol,1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-hexylene glycol,1,10-decanediol, 1,2-cyclohexanediol, 2-butene-1,4-diol,3-cyclohexene-1,1-dimethanol, 4-methyl-3-cyclohexene-1,1-dimethanol,3-methylene-1,5-pentanediol, diethylene glycol,(2-hydroxyethoxy)-1-propanol, 4-(2-hydroxyethoxy)-1-butanol,5-(2-hydroxypropoxy)-1-pentanol, 1-(2-hydroxymethoxy)-2-hexanol,1-(2-hydroxypropoxy)-2-octanol, 3-allyloxy-1,5-pentanediol,2-allyloxymethyl-2-methyl-1,3-propanediol,[4,4-pentyloxy)-methyl]-1,3-propanediol,3-(o-propenylphenoxy)-1,2-propanediol,2,2′-diisopropylidenebis(p-phenyleneoxy)diethanol, glycerol,1,2,6-hexanetriol, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane,3-(2-hydroxyethoxy)-1,2-propanediol,3-(2-hydroxypropoxy)-1,2-propanediol,2,4-dimethyl-2-(2-hydroxyethoxy)-methylpentanediol-1,5;1,1,1-tris[2-hydroxyethoxy)methyl]-ethane,1,1,1-tris[2-hydroxypropoxy)-methyl]propane, diethylene glycol,dipropylene glycol, pentaerythritol, sorbitol, sucrose, lactose,alpha-methylglucoside, alpha-hydroxyalkylglucoside, novolac polymers,phosphoric acid, benzenephosphoric acid, polyphosphoric acids such astripolyphosphoric acid and tetrapolyphosphoric acid, ternarycondensation products, and the like. The alkylene oxides used inproducing polyoxyalkylene polyols normally have from 2 to 4 carbonatoms. Exemplary alkylene oxides are propylene oxide and mixtures ofpropylene oxide with ethylene oxide. Polytetramethylene polyether diolor glycol, and mixture with one or more other polyols, can bespecifically mentioned. The polyols listed above can be used per se asthe active hydrogen component.

A specific class of polyether polyols is represented generally by theformula R[(OC_(n)H_(2n))_(z)OH]_(a) wherein R is hydrogen or apolyvalent hydrocarbon radical; a is an integer (i.e., 2 to 8) equal tothe valence of R, n in each occurrence is an integer from 2 to 4inclusive (preferably 3) and z in each occurrence is an integer having avalue of 2 to 200, preferably 15 to 100. Specifically, the polyetherpolyol can have the formula R[(OC₄H₈)_(z)OH]₂, wherein R is a divalenthydrocarbon radical and z in each occurrence is 2 to about 40,specifically 5 to 25.

Another type of active hydrogen-containing material that can be used isa polymer polyol composition obtained by polymerizing ethylenicallyunsaturated monomers with a polyol as described in U.S. Pat. No.3,383,351, the disclosure of which is incorporated herein by reference.Suitable monomers for producing such compositions include acrylonitrile,vinyl chloride, styrene, butadiene, vinylidene chloride, and otherethylenically unsaturated monomers as identified and described in theabove-mentioned U.S. patent. Suitable polyols include those listed anddescribed hereinabove and in U.S. Pat. No. 3,383,351. The activehydrogen-containing component may also contain polyhydroxyl-containingcompounds such as hydroxyl-terminated polyhydrocarbons (U.S. Pat. No.2,877,212); hydroxyl-terminated polyformals (U.S. Pat. No. 2,870,097);fatty acid triglycerides (U.S. Pat. Nos. 2,833,730 and 2,878,601);hydroxyl-terminated polyesters (U.S. Pat. Nos. 2,698,838, 2,921,915,2,591,884, 2,866,762, 2,850,476, 2,602,783, 2,729,618, 2,779,689,2,811,493, 2,621,166 and 3,169,945); hydroxymethyl-terminatedperfluoromethylenes (U.S. Pat. Nos. 2,911,390 and 2,902,473);hydroxyl-terminated polyalkylene ether glycols (U.S. Pat. No. 2,808,391;British Patent No. 733,624); hydroxyl-terminated polyalkylenearyleneether glycols (U.S. Pat. No. 2,808,391); and hydroxyl-terminatedpolyalkylene ether triols (U.S. Pat. No. 2,866,774).

In a specific embodiment, the active hydrogen-containing componentcomprises a higher molecular weight polyether polyol and/or polyesterpolyol and a very low molecular weight polyol as a chain extender orcrosslinking agent. Preferred polyether polyols include polyoxyalkylenediols and triols, and polyoxyalkylene diols and triols with polystyreneand/or polyacrylonitrile grafted onto the polymer chain, and mixturesthereof. Preferred polyester polyols are based on caprolactone.

Exemplary very low molecular weight chain extenders and cross-linkingagents include alkane diols and dialkylene glycols and/or polyhydricalcohols, preferably triols and tetrols, having a molecular weight fromabout 200 to 400. The chain extenders and cross-linking agents are usedin amounts from about 0.5 to about 20 percent by weight, preferably fromabout 10 to 15 percent by weight, based on the total weight of theactive-hydrogen-containing component.

Thus, in one embodiment, the polyol component comprises a polymeric diolhaving a weight average molecular weight of from about 650 to about2900, specifically of between 1000 and 2800, more specifically 1500 to2500. The polymeric diol can have a hydroxy number of 10 to 200,preferably a hydroxy number of 15 to 50, more preferably 20 to 40. Apreferred polymeric diol is a polyoxyalkylene polyol. In a specificembodiment, the polymeric diol is a polyether oxide diol, morespecifically a polyether glycol. The use of polytetramethylene etherglycol was found advantageous for improved abrasion compared to otherdiols.

The polyol can further comprise a triol. In one embodiment, the triolhas a weight average molecular weight (Mw) that is 80 to 2000,preferably 100 to 1000, more preferably 150 to 400. (Unless otherwiseherein indicated, all molecular weights are weight average molecularweights.) The hydroxy number can be 200 to 2000, preferably 500 to 1500.A preferred triol is a polycaprolactone triol.

In another embodiment, the polyol component further comprises a very lowmolecular weight (below about 200) diol, including but not being limitedto, dipropylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and3-methyl-1,5-pentane diol. This compound can function as a chainextender in the reaction mixture for the polyurethane.

In one embodiment, the reaction mixture for forming the polyurethanecomprises a polymeric diol, triol, and a low molecular weight diol as achain extender, in combination with a polyisocyanate prepolymer. In thisembodiment, the weight average molecular weights of the polymeric diolis greater than that of the triol and diol compound by at least about1000. Specifically, the active hydrogen-containing component comprisesabout 50 to about 90 parts by weight (pbw) of the polymeric diol,specifically a polyether glycol, about 5 to about 25 pbw of a triol,specifically a triol having an Mw of about 80 to about 2000, and about 1to about 25 pbw of a chain extender. In another embodiment, the activehydrogen-containing component comprises about 60 to about 80 parts byweight (pbw) of the polymeric diol, specifically a polyether glycol,about 10 to about 20 pbw of a triol, and about 1 to about 20 pbw of achain extender.

In general, the average wt. percent hydroxy, based on the hydroxylnumbers of the hydroxyl-containing compounds (including all polyols ordiols), including other cross-linking additives, fillers, surfactants,catalysts and pigments, if used, can be about 150 to about 350 invarious embodiments, depending on the desired firmness or softness ofthe polishing pad for a particular application. For example, arelatively firmer pad can have a total hydroxy number of 300-350, asofter pad can have a total hydroxy number of 150-200, and a mid-rangepad can have a hydroxy number of 200 to 300. The hydroxyl number isdefined as the number of milligrams of potassium hydroxide required forthe complete neutralization of the hydrolysis product of the fullyacetylated derivative prepared from 1 gram of polyol or mixtures ofpolyols with or without other cross-linking additives. The hydroxylnumber can also be defined by the equation:

${OH} = \frac{56.1 \times 1000 \times f}{M.W.}$

wherein OH is the hydroxyl number of the polyol, f is the averagefunctionality that is the average number of hydroxyl groups per moleculeof polyol, and M.W. is the average molecular weight of the polyol.

The particular polyol components, i.e., the molecular weights and thehydroxyl number are further selected so as to provide a molecular weightbetween crosslinks of about 2,000 to about 10,000 Daltons, preferablyabout 3,000 to about 6,000 Daltons. The molecular weight betweencrosslinks (M_(c)) is calculated by dividing the total weight ofmaterial by the sum of the moles of each reactive component eachmultiplied by its functionality minus 2.

A wide variety of surfactants can be used for stabilizing thepolyurethane foam before it is cured, including mixtures of surfactants.An organosilicone surfactant, for example, is a copolymer consistingessentially of SiO₂ (silicate) units and (CH₃)₃SiO_(0.5)(trimethylsiloxy) units in a molar ratio of silicate to trimethylsiloxyunits of about 0.8:1 to about 2.2:1, specifically about 1:1 to about2.0:1. Another organosilicone surfactant stabilizer is a partiallycross-linked siloxane-polyoxyalkylene block copolymer and mixturesthereof wherein the siloxane blocks and polyoxyalkylene blocks arelinked by silicon to carbon, or by silicon to oxygen to carbon,linkages. The siloxane blocks comprise hydrocarbon-siloxane groups andhave an average of at least two valences of silicon per block combinedin said linkages. At least a portion of the polyoxyalkylene blockscomprise oxyalkylene groups and are polyvalent, i.e., have at least twovalences of carbon and/or carbon-bonded oxygen per block combined insaid linkages. Any remaining polyoxyalkylene blocks comprise oxyalkylenegroups and are monovalent, i.e., have only one valence of carbon orcarbon-bonded oxygen per block combined in said linkages. A combstructure can also be used with a polydimethylsiloxane backbone andsoluble pendent groups. Additionally, conventionalorganopolysiloxane-polyoxyalkylene block copolymers such as thosedescribed in U.S. Pat. Nos. 2,834,748; 2,846,458; 2,868,824; 2,917,480;and 3,057,901 can be used. The amount of the organosilicone polymer usedas a foam stabilizer can vary, e.g., 0.5 wt. % to 10 wt. % parts orgreater based on the amount of the active hydrogen component. The amountof organosilicone surfactant in the polyurethane formulations, in oneembodiment, is about 1.0 wt. % to about 6.0 wt. % on the same basis.

A number of the catalysts conventionally used to catalyze the reactionof the isocyanate component with the active hydrogen-containingcomponent can be used in the foam preparation. Such catalysts includeorganic and inorganic acid salts of, and organometallic derivatives of,bismuth, lead, tin, iron, antimony, uranium, cadmium, cobalt, thorium,aluminum, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper,manganese, and zirconium, as well as phosphines and tertiary organicamines. Examples of such catalysts are dibutyltin dilaurate, dibutyltindiacetate, stannous octoate, lead octoate, cobalt naphthenate,triethylamine, triethylenediamine, N,N,N′,N′-tetramethylethylenediamine,1,1,3,3-tetramethylguanidine, N,N,N′N′-tetramethyl-1,3-butanediamine,N,N-dimethylethanolamine, N,N-diethylethanolamine,1,3,5-tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine, o- andp-(dimethylaminomethyl) phenols, 2,4,6-tris(dimethylaminomethyl) phenol,N,N-dimethylcyclohexylamine, pentamethyldiethylenetriamine,1,4-diazobicyclo[2.2.2]octane, N-hydroxyl-alkyl quaternary ammoniumcarboxylates and tetramethylammonium formate, tetramethylammoniumacetate, tetramethylammonium 2-ethylhexanoate, and the like, as well ascompositions comprising any one of the foregoing catalysts.

Metal acetyl acetonates are preferred, based on metals such as aluminum,barium, cadmium, calcium, cerium (III), chromium (III), cobalt (II),cobalt (III), copper (II), indium, iron (II), lanthanum, lead (II),manganese (II), manganese (III), neodymium, nickel (II), palladium (II),potassium, samarium, sodium, terbium, titanium, vanadium, yttrium, zincand zirconium. A specific catalyst is bis(2,4-pentanedionate) nickel(II) (also known as nickel acetylacetonate or diacetylacetonate nickel)and derivatives thereof such as diacetonitrilediacetylacetonato nickel,diphenylnitrilediacetylacetonato nickel, bis(triphenylphosphine)diacetylacetylacetonato nickel, and the like. Ferric acetylacetonate (FeAA) hasgood relative stability, good catalytic activity, and lack of toxicity.

In one embodiment acetyl acetone (2,4-pentanedione) is added to a metalacetyl acetonate (or other catalyst), as disclosed in commonly assignedU.S. Pat. No. 5,733,945 to Simpson, which is incorporated herein byreference. The acetyl acetone provides heat latency, which allows timefor the required mixing, casting, and other procedures, and avoidsdeleterious premature curing during low temperature processing. However,as the material is cured in several heating zones and the temperature ofthe urethane mixture rises, the acetyl acetone is driven off. With theremoval of acetyl acetone together with its associated delayingfunction, the metal acetyl acetonate is allowed to resume its normallyhigh reactivity and provide a very high level of catalysis at the end ofthe polyurethane reaction. This high reactivity late in the processingcycle is advantageous and provides improved physical properties such ascompression set. In this embodiment, the ratio of metal acetyl acetonateto acetyl acetone is about 2:1 on a weight basis.

The amount of catalyst present in the reactive composition can be about0.03 wt % to about 3.0 wt %, based on the weight of the activehydrogen-containing component.

In one embodiment, when water is used as the blowing agent, FeAA isselected as the catalyst. Other catalysts or adjuvants, e.g., amines,can be used to adjust the relative reaction rates of water and urethane.The water reacts with the isocyanate releasing CO₂. The use of FeAA withacetyl acetone catalyzes the curing reaction in a delayed fashion, whichprevents premature curing and therefore allows the chemical (andoptionally physical) blowing to continue unhindered. The catalysteventually permits a full cure of the polyurethane foam. The metalacetylacetonate is most conveniently added by predissolution in asuitable solvent such as dipropylene glycol or other hydroxyl containingcomponents which will then participate in the reaction and become partof the final product.

The polyurethane-forming composition can further comprise other optionaladditives depending on the desired properties of the polishing pad, forexample, its abrasive or other properties, and its particular use as apolishing pad on various work pieces. Exemplary additives include dyes,pigments (for example, titanium dioxide and iron oxide), antioxidants,antiozonants, flame retardants, UV stabilizers, conductive fillers,conductive polymers, and the like.

The polishing pad can optionally contain additional particles, e.g.,particles other than the above-described hydrophobic particles that areincorporated into the material of the pad. The particles can be abrasiveparticles, polymer particles, composite particles (e.g., encapsulatedparticles), organic particles, inorganic particles, clarifyingparticles, water-soluble particles, and mixtures thereof. The polymerparticles, composite particles, organic particles, inorganic particles,clarifying particles, and water-soluble particles can be abrasive, ornon-abrasive, in nature. The abrasive particles, for example, can be ametal oxide, such as a metal oxide selected from the group consisting ofalumina, silica, titania, ceria, zirconia, germania, magnesia, co-formedproducts thereof, and combinations thereof, or a silicon carbide, boronnitride, diamond, garnet, or ceramic abrasive material. The abrasiveparticles can be hybrids of metal oxides and ceramics or hybrids ofinorganic and organic materials. The particles also can be polymerparticles such as polystyrene particles, polymethylmethacrylateparticles, liquid crystalline polymers (LCP, e.g., aromatic copolyesterscontaining naphthalene units), polyetheretherketones (PEEK's),particulate thermoplastic polymers (e.g., particulate thermoplasticpolyurethane), particulate cross-linked polymers (e.g., particulatecross-linked polyurethane or polyepoxide), or a combination thereof, asdescribed in U.S. Pat. No. 7,204,742. The composite particles contain asolid core (e.g., a metal oxide, metal, ceramic, or polymer) and apolymeric shell (e.g., polyurethane, nylon, or polyethylene). Theclarifying particles can be phyllosilicates, (e.g., micas such asfluorinated micas, and clays such as talc, kaolinite, montmorillonite,hectorite), glass fibers, glass beads, diamond particles, carbon fibers,and the like.

Small amounts of water or an auxiliary blowing agent can be present inthe polyurethane-forming compositions. For example, high-boilingfluorocarbons, e.g., those boiling above about 40° C. can be used.Specific fluorocarbons include the Ucon fluorocarbons and FREONS boilingabove about 40° C., for example 1,1,2-trichloro-1,2,2-trifluoroethaneand isomers of tetrachlorodifluoroethane, tetrachloromonofluoroethane,and the like. The auxiliary agent, although it is not necessary, can beused for purposes of providing an added expansion during heat curing inthose cases where such added expansion is desired.

The foamed material is produced by mechanically mixing the reactivecomposition (i.e., isocyanate component, active hydrogen-containingcomponent, hydrocarbon particles, froth-stabilizing surfactant, catalystand other optional additives) with a froth-forming gas in apredetermined amount. An inert gas is incorporated into the liquid phaseby mechanical beating of the liquid phase in high shear equipment suchas a Hobart mixer or an Oakes mixer. Mechanical blowing is preferred, asit is more likely to lead to spherical cells than chemically blownfoams. The gas phase of the froths is most preferably air because of itscheapness and ready availability. However, if desired, other gases canbe used which are gaseous at ambient conditions and which aresubstantially inert or non-reactive with any component of the liquidphase. Such other gases include, for example, nitrogen, carbon dioxide,and fluorocarbons that are normally gaseous at ambient temperatures. Thegas can be introduced under pressure as in the usual operation of anOakes mixer or it can be drawn in from the overlying atmosphere by thebeating or whipping action as in a Hobart mixer. The mechanical beatingoperation preferably is conducted at pressures not greater than 100 to200 psig (pounds force per square inch gauge). Conventional, readilyavailable mixing equipment can be used and no special equipment isnecessary. The amount of inert gas beaten into the liquid phase shouldbe adequate to provide a froth having a density at ambient atmosphericpressure of about 30 to about 60 pcf (pounds per cubic foot),specifically about 45 to about 55 pcf and less than about 50% to about90% of the density of the liquid phase prior to frothing. The mechanicalbeating can be conducted over a period of a few seconds in an Oakesmixer, or for about 3 to 30 minutes in a Hobart mixer, or however longit takes to obtain the desired froth density in the mixing equipmentemployed. The froth as it emerges from the mechanical beating operationis substantially chemically stable and is structurally stable but easilyworkable at ambient temperatures, e.g., about 15° C. to about 30° C. Theconsistency of the froth resembles the consistency of aerosol-dispensedshaving cream.

The frothed mixture can be continuously fed onto a substrate film, whichcan also be utilized as transfer means in the production process. Asubstrate film can also be referred to herein as a first carrier orbottom carrier layer, but it can also be stationary, depending on theparticular process. Furthermore, the upper side of the frothed mixturecan be provided with a surface protective film, also referred to hereinas a second or top carrier. Thus, if desired, the frothed reactivecomposition can be sandwiched between upper and lower two films, andshaped into a sheet form with its surface protected from roughening andits thickness controlled, whereby a foamed polyurethane sheet isproduced from which the polishing pad can be formed.

In another embodiment, the foam may be produced by a combination ofmechanical frothing and blowing. In one manner of proceeding, thecomponents for producing the low density foams, i.e., the isocyanatecomponent, the active hydrogen containing component, hydrophobicparticles, catalyst, blowing agents and any other additives are firstmixed together and then subjected to mechanical frothing with air.Alternatively, the components may be added sequentially to the liquidphase during the mechanical frothing process.

In practice, a substrate or carrier can be played out from supply rollsand ultimately rewound on take-up rolls upon separation from the curedpolyurethane foam. The selection of materials for the substrate candepend on factors such as the desired degree of support and flexibility,the desired degree of releasability from the cured foam, cost, and thelike considerations. Paper, thin sheets of metal such as stainlesssteel, or polymer films such as polyethylene terephthalate, silicone, orthe like can be used. The material can be coated with a release coating.In one embodiment, the substrate can be coated with a material intendedto be transferred to the surface of the cured polyurethane foam, forexample a polyurethane film that is releasable from the substrate. Afibrous web or other filler material can be disposed on the surface ofthe substrate, and thereby become ultimately incorporated into the curedfoam. In another embodiment, the foam cures to a substrate. Thus, asubstrate can be optionally part of the final product, instead of beingseparated from the foam. In one embodiment, a conveyor belt can be usedas a substrate and have a plain or a textured surface.

In a specific embodiment, in order to enhance the structural strength ofan article such as a chemical-mechanical polishing pad and to improvethe handling properties of the product, a substrate film is cured to apolyurethane foam sheet, i.e., is bound to the polyurethane sheet. Ashereinafter described with respect to a production method, thissubstrate film can also serve as a transfer means for the frothedreactive composition in a production apparatus, such as described inU.S. Pat. No. 7,338,983. Therefore, the substrate film can be a polymerhaving low heat-shrinkable properties, such as polyethyleneterephthalate (PET), the polymer having a physical strength resistibleto a tensile force applied by a roller machine, and resistanceproperties to heat applied by a heating means. In addition, a filmcomprising a polymer such as polyolefin, polyester, polyamide, orpolyvinyl chloride can be also used. The thicknesses of the films willnot adversely affect the polishing properties of the article even whenthe substrate film is bonded to a polyurethane foam sheet.

In a specific embodiment, the foam is cast onto a first layer of apolyurethane foam, as in U.S. Pat. No. 6,884,156 to Cabot or U.S. Pat.No. 6,635,688 to World Properties, Inc. The foam pad can be integrallybonded, or laminated using an adhesive, to form a composite structure.In another embodiment, the polishing pad can be a composite padcomprising an unfrothed top polishing pad that is simultaneously castwith a mechanically frothed subpad.

In one embodiment, after the polyurethane material is cast onto asubstrate, the composition (after optional blowing) is delivered to aheating zone for cure of the polyurethane foams. The temperatures aremaintained in a range suitable for curing the foam, for example at about90° C. to about 220° C., depending on the composition of the foammaterial. Differential temperatures can be established for purposes offorming an integral skin on an outside surface of the foam.

After the foam is heated and cured, it can then be passed to a coolingzone where it is cooled by any suitable cooling device such as fans. Inone embodiment, where appropriate, the substrate is removed and the foamcan be taken up on a roll. Alternatively, the foam can be subjected tofurther processing, for example lamination (bonding using heat andpressure) to a substrate, if desired.

In a final step, in one embodiment, a long, foamed polyurethane sheet isobtained, which can be punched out in the shape of a CMP pad as a finalproduct. A final inspection can then be carried out. Alternatively, thefoamed polyurethane sheet may be cut into individual sheets, while afinal inspection is carried out, so as to be shipped in its currentfinal shape for later processing into individual CMP pads. The thicknessof the cured polyurethane foam is about 0.5 to about 5.0 mm,specifically about 1.0 to about 3.0 mm.

The polishing layer can be modified by buffing or conditioning, such asby moving the pad against an abrasive surface. The preferred abrasivesurface for conditioning is a disk which is preferably metal and whichis preferably embedded with diamonds of a size in the range of 1 μm to0.5 mm. Optionally, conditioning can be conducted in the presence of aconditioning fluid, preferably a water-based fluid containing abrasiveparticles.

The polishing layer further comprises grooves, channels, and/orperforations. Such features can facilitate the lateral transport of apolishing composition across the surface of the polishing layer. Thegrooves, channels, and/or perforations can be in any suitable patternand can have any suitable depth and width. The polishing pad substratecan have two or more different groove patterns, for example acombination of large grooves and small grooves as described in U.S. Pat.No. 5,489,233. The grooves can be in the form of linear grooves, slantedgrooves, concentric grooves, spiral or circular grooves, or XYcrosshatch pattern, and can be continuous or non-continuous inconnectivity. The polishing pad substrate optionally further comprisesone or more apertures, transparent regions, or translucent regions(e.g., windows as described in U.S. Pat. No. 5,893,796). The inclusionof such apertures or translucent regions (i.e., optically transmissiveregions) is desirable when the polishing pad substrate is to be used inconjunction with an in situ CMP process monitoring technique.

The performance of the polishing pad material can also be influenced andsometimes controlled through other physical properties of the polishingpad, although pad performance is also dependent on all aspects of thepolishing process and the interactions between pad, slurry, polishingtool, and polishing conditions, for example.

In order to provide desired mechanical properties to the foam,particularly superior polishing properties for a polyurethane foam, theaverage cellular diameter of the foam can be about 20 to about 150micrometers, preferably about 50 to about 100 micrometers.

In one embodiment, the polishing pads have a density of 30 to 65 poundsper cubic foot (pcf), or 480 to 1040 kilograms per cubic meter (kg/m³),specifically 40 to 60 pcf, (640 to 960 kg/m³).

Surface roughness values are measured after conditioning. In someembodiments, the polishing pad has a surface roughness of about 2 toabout 25 micrometer Ra, specifically about 3 to about 20 micrometer Ra.

The polishing pads can have a hardness of about 45 to about 65 Shore D.In yet other embodiments, the polishing pads have a hardness of about 55to about 63 Shore D.

In one embodiment, the surface energy of the polishing pad aftergrinding can be about 15 to about 50 mN/m, specifically about 20 toabout 40 mN/m, more specifically about 30 to about 35 mN/m, based on theFowkes Method employing the Sessile drop contact-angle measurementtechnique. For this embodiment, the skin surface of the polyurethanematerial, as produced (before grinding) can be about 10 to about 35mN/m, specifically about 15 to about 30 mN/m, more specifically about 20to about 25 mN/m, based on the Fowkes Method employing the Sessile dropcontact-angle measurement technique, as described in the Examples below.

The polishing pads can be characterized by techniques of dynamicmechanical analysis (as described in J. D. Ferry, “ViscoelasticProperties of Polymers”, New York, Wiley. 1961 which is herebyincorporated by reference in its entirety). Viscoelastic materialsexhibit both viscous and elastic behavior in response to an applieddeformation. The resulting stress signal can be separated into twocomponents: an elastic stress which is in phase with the strain, and aviscous stress which is in phase with the strain rate but 90 degrees outof phase with the strain. The elastic stress is a measure of the degreeto which a material behaves as an elastic solid; the viscous stressmeasures the degree to which the material behaves as an ideal fluid. Theelastic and viscous stresses are related to material properties throughthe ratio of stress to strain (this ratio can be defined as themodulus). Thus, the ratio of elastic stress to strain is the storage (orelastic) modulus and the ratio of the viscous stress to strain is theloss (or viscous) modulus. When testing is done in tension orcompression, E′ and E″ designate the storage and loss modulus,respectively.

The ratio of the loss modulus to the storage modulus is the tangent ofthe phase angle shift (δ) between the stress and the strain. Accordingto the equation, E″/E′=tan δ and is a measure of the damping ability ofthe material.

In addition to the parameter tan δ, as defined above, another parameterfor predicting polishing performance is known as the “Energy LossFactor,” ASTM D4092-90 (“Standard Terminology Relating to DynamicMechanical Measurements of Plastics”), incorporated by reference in itsentirety, which defines this parameter as the energy per unit volumelost in each deformation cycle. In other words, it is a measure of thearea within the stress-strain hysteresis loop.

The Energy Loss Factor (KEL) is a function of both tan δ and the elasticstorage modulus (E′) and may be defined by the following equation:

KEL=tan δ*10 ¹² /[E′*(1+tan δ²)]

wherein E′ is in Pascals.

The higher the value of KEL for a pad, generally the lower the elasticrebound. During the polishing cycle, energy is transmitted to the pad. Aportion of this energy is dissipated as heat, and the remaining portionis stored in the pad and subsequently released as elastic energy duringthe polishing cycle. Generally, the higher the value of KEL for a pad,the lower the elastic rebound. To increase the KEL value, the pad can bemade softer. However, this approach can tend to reduce the stiffness ofthe pad, resulting in decreased polishing efficiency as well as otherpotential problems.

The storage modulus (E′) and Energy Loss Factor (KEL) can be measuredusing the method of Dynamic Mechanical Analysis at a temperature of 0°C., 20° C., 40° C., 50° C. and 70° C., and frequency of 10 radians/sec.KEL is calculated using the equation defined above. The ratio of theModulus or KEL can also be measured at various temperatures, especiallyat temperatures that represent the useful temperature range forpolishing. Ideally, Modulus or KEL will change as little as possible andin a linear trend with increasing temperature (i.e. a ratio of thevalues at two temperatures approaches unity).

In one embodiment, the polyurethane polishing layer exhibits a storagemodulus (E′) of greater than about 100 MPa, specifically about 100 toabout 1000 MPa, each over a range of 20° C. to 50° C. Such firmerpolishing pads are useful as, e.g., a copper or oxide polishing pad. Inanother embodiment, the polyurethane layer exhibits a storage modulus(E′) of about 40 to about 200 MPa over a range of 20° C. to 50° C. Thesesofter pads are useful, e.g., as a barrier polishing pad. In either ofthe foregoing embodiments, the polyurethane layer can exhibit a ratio ofE at 50° C.:E at 20° C. of less than 1.0, specifically about 0.5 toabout 0.8. In yet other embodiments, the polishing pads have a storagemodulus E of 250 to 650 MPa in the range of 20° C. to 50° C.,specifically 300 to 600 MPa at 40° C.

In one embodiment the polyurethane layer can exhibit a KEL of about 1 toabout 500 1/Pa, specifically about 10 to about 400 1/Pa at 50° C., morespecifically about 50 to about 300, each in the range of 20° C. to 50°C. In yet other embodiments, the polyurethane layer can have a KEL of100 to 250 1/Pa at 50° C. These ranges are suitable for a firmerpolishing pad that can be used, e.g., for copper or oxide polishing. Itis also possible to manufacture polishing pads having a KEL of greaterthan about 1,000 at 50° C., which can be useful for, e.g., barrierpolishing pads. In any of the foregoing embodiments, the polyurethanelayer can have a ratio of KEL at 50° C.:KEL at 20° C. of less than 5.0,specifically 1.0 to 4.0.

The polyurethane can exhibit a tan δ of less than 0.070 in the range of20° C. to 50° C. The polyurethane can exhibit a ratio of tan δ at 50°C.:tan δ at 20° C. of 1.2 to 3.0. Again without wishing to be bound bytheory, it is believed that the improved performance of the polishingpads, in particular the lower polishing temperatures, are due to the lowtan delta (higher resilience) of the polishing pads described herein. Itis believed that the higher resilience provides polishing performancewith faster recovery between polishing passes, and lower heat generationthan less resilient polishing pads. Since less energy is converted toheat, lower polishing temperatures result. Further, since the ratio ofthe modulus and the tan delta is flat between 20 and 50° C., theperformance of the polishing pads is consistent in this temperaturerange.

The polishing pad is characterized by a lower defect rate during use. Asdemonstrated in the examples, a defect rate of less than 3500,specifically less than 2000, more specifically less than 1500 can beobtained based on a 0.25 μm cutoff. A defect rate of less than 20000,specifically less than 10000, more specifically less than 5000 can beobtained at a 0.20 um cutoff.

The polishing pad can be used alone, or optionally can be mated to a padcarrier. When the polishing pad is mated to the pad carrier, thepolishing pad is intended to contact the work piece to be polished andserves as the polishing layer, while the substrate serves as a subpad.

In a specific embodiment, the foam is cast onto a first, uncured layerof a polyurethane foam, as described in U.S. Pat. No. 6,635,688 to WorldProperties, Inc. Subsequent curing of both pads provides an integrallybonded composite polishing pad.

Other exemplary subpads include polyurethane foam subpads, impregnatedfelt subpads, microporous polyurethane subpads, and sintered urethanesubpads. The polishing layer and/or the subpad optionally comprisesgrooves, channels, hollow sections, windows, apertures, and the like.The subpad can be affixed to the polishing layer by any suitable means.For example, the polishing layer and subpad can be affixed throughadhesives or can be attached via welding or similar technique. Anintermediate backing layer such as a poly(ethylene terephthalate) filmcan be disposed between the polishing layer and the subpad.

These substrates for the pad can be produced by means known in the art.For example, the pad substrate can be produced by extruding one of theaforesaid polymers. The extruded copolymer or polymer can optionally bemodified to increase the porosity or void volume.

The polishing pad is particularly suited for use in conjunction with achemical-mechanical polishing (CMP) apparatus. Typically, the apparatuscomprises a platen, which, when in use, is in motion and has a velocitythat results from orbital, linear, or circular motion. The polishing padsubstrate is in contact with the platen and moves with the platen whenin motion. The apparatus can further comprise a carrier that holds awork piece to be polished by contacting, and moving relative thereto,the polishing surface of the polishing pad. The polishing of the workpiece typically takes place with a polishing composition introducedbetween the work piece and the polishing pad as they move relative toeach other, so as to abrade at least a slight portion of the work piecein order to polish the work piece. The CMP apparatus can be any suitableCMP apparatus, many of which are known in the art. The polishing padalso can be used with linear polishing tools.

In one particular embodiment of polishing surfaces, a conventionalpolishing machine employs a down force of 35 to 700, preferably 70 to500 g/cm² (0.5 to 10 psi, specifically 1 to 6 psi), a platen speed of 25to 400 rpm, preferably 50 to 200 rpm, a carrier speed of 25 to 400 rpm,preferably 50 to 200 rpm, and a media flow of 20 to 500, specifically100 to 200 ml/min.

The working film, or surface layer of the work piece, that is thesubject of chemical mechanical polishing according to the presentinvention can be a silicon oxide film, amorphous silicon film,polycrystalline silicon film, single-crystal silicon film, siliconnitride film, pure tungsten film, pure aluminum film or pure copperfilm, or an alloy film of tungsten, aluminum or copper with anothermetal, formed on a wafer during manufacture of a semiconductor devicesuch as a VLSI or the like. The working film may also be an oxide ornitride film of a metal, for example, tantalum or titanium.

When the surface of the working film is a metal, the polishing rate canbe vastly improved by adding an oxidizing agent to the polishingcomposition applied during the polishing operation. The oxidizing agentused can be appropriately selected, for example, based on theelectrochemical properties of the working surface.

Other work pieces that can be polished with the polishing pad includememory storage devices, glass substrates, memory or rigid disks, metals(e.g., noble metals), magnetic heads, inter-layer dielectric (ILD)layers, polymeric films (e.g., organic polymers), low and highdielectric constant films, ferroelectrics, micro-electro-mechanicalsystems (MEMS), field emission displays, and other microelectronic workpieces, especially microelectronic work pieces comprising insulatinglayers (e.g., a metal oxide, silicon nitride, or low dielectricmaterial) and/or metal-containing layers (e.g., copper, tantalum,tungsten, aluminum, nickel, titanium, platinum, ruthenium, rhodium,iridium, silver, gold, alloys thereof, and mixtures thereof). The term“memory or rigid disk” refers to any magnetic disk, hard disk, rigiddisk, or memory disk for retaining information in electromagnetic form.Memory or rigid disks typically have a surface that comprisesnickel-phosphorus, but the surface can comprise any other suitablematerial. Suitable metal oxide insulating layers include, for example,alumina, silica, titania, ceria, zirconia, germania, magnesia, andcombinations thereof. In addition, the work piece can comprise, consistessentially of, or consist of any suitable metal composite. Suitablemetal composites include, for example, metal nitrides (e.g., tantalumnitride, titanium nitride, and tungsten nitride), metal carbides (e.g.,silicon carbide and tungsten carbide), metal silicides (e.g., tungstensilicide and titanium silicide), nickel-phosphorus,alumino-borosilicate, borosilicate glass, phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), silicon/germanium alloys, andsilicon/germanium/carbon alloys. The work piece also can comprise,consist essentially of, or consist of any suitable semiconductor basematerial. Suitable semiconductor base materials include monocrystallinesilicon, polycrystalline silicon, amorphous silicon,silicon-on-insulator, and gallium arsenide. The work piece can comprisea metal layer, more preferably a metal layer selected from the groupconsisting of copper, tungsten, tantalum, platinum, aluminum, andcombinations thereof.

The polishing pad can be used for applications where the surface beingpolished is susceptible to damage. In one embodiment, the method is usedin the microelectronics industry to remove excess metal and/ordielectrics from integrated circuits, for example, on a wafer. Inparticular, removal of selected layers from an integrated circuit isfacilitated, i.e., the polishing pad as described herein improves theremoval process without damaging the delicate printed circuit lines orthe underlying substrate material.

A wide variety of polishing compositions can be used with the polishingpad. Such compositions typically comprise a liquid carrier (e.g., water,or a mixed medium containing an organic solvent such as an alcohol incombination with water), an abrasive (e.g., alumina, silica, titania,ceria, zirconia, germania, magnesia, and combinations thereof), andoptionally one or more additives such as oxidizing agents (e.g.,peracetic acid, perbenzoic acid, tertbutylhydroperoxide, hydrogenperoxide, ammonium persulfate, potassium permanganate, potassiumbichromate, potassium iodate, perchloric acid, potassium ferricyanide,iron nitrate, cerium ammonium nitrate, silicotungstic acid,phosphotungstic acid, silicomolybdic acid, and phosphomolybdic acid),corrosion inhibitors (e.g., benzotriazole), film-forming agents (e.g.,polyacrylic acid and polystyrenesulfonic acid), complexing agents (e.g.,mono-, di-, and poly-carboxylic acids, phosphonic acids, and sulfonicacids), chelating agents (e.g., triazole, indole, benzimidazole,benzoxazole-benzotriazole, quinoline, quinolinic acid, quinoxaline,benzoquinoline, benzoxidine, ammonia, ethylenediamine, triethanolamine,glycine, alanine, leucine, glutamine, glutamic acid, tryptophan,5-amino-1H-tetrazole, 7-hydroxy-5-methyl-1,3,4-triazaindolazine,benzoguanamine, salicylaldoxime, adenine, guanine, phthalazine,5-methyl-1H-benzotriazole, and 4-amino-1,2,4-triazole), organic acids(e.g., para-toluenesulfonic acid, dodecylbenzenesulfonic acid,isoprenesulfonic acid, gluconic acid, lactic acid, citric acid, tartaricacid, malic acid, glycolic acid, malonic acid, formic acid, oxalic acid,succinic acid, fumaric acid, maleic acid, and phthalic acid), pHadjusters (e.g., hydrochloric acid, sulfuric acid, phosphoric acid,sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesiumhydroxide, and ammonium hydroxide), buffering agents (e.g., phosphatebuffers, acetate buffers, and sulfate buffers), ionic or non-ionicsurfactants, deflocculants, viscosity modifiers, wetting agents,cleaning agents, and combinations thereof. The selection of thecomponents of the polishing composition, which can be used with thepolishing pad, and the relative amounts thereof, depends primarily onthe type of work piece being polished. It will be appreciated that thecomponents of a slurry can be combined in various ways to form theslurry in situ.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLES

In the following examples, the materials shown in Table 1 were used.

TABLE 1 Component Description and Trade Name Supplier PTMEGPoly(tetramethylene ether) diol or glycol having a Invista hydroxylnumber of about 56 (Terethane 2000) (Polymeric polyol) MP diol2-Methyl-1,3-propanediol (chain extender) — Triol Polycaprolactonetriol, weight average molecular Perstop Ltd. weight (M_(w)) = 300, OHvalue (mg KOH/g) = 560 (Cheshire, UK) (CAPA 3031) Isocyanate MDIprepolymer, a modified MDI compound Dow Chemical produced by reactinghigh-purity diphenylmethane Co. diisocyanate with sufficient glycol toallow handling (Midland, MI) down to 80° F. (ISONATE ™ 181) HydrophobicPoly(tetrafluoroethylene), granular powder having a Asahi (Japan)Particle particle size of 25.0 micrometers, bulk density of 0.330 g/cc,tensile strength at break of 42.0 MPa and elongation at break of 350%(Fluon ® G163 PTFE) Surfactant Silicon surfactant and stabilizer (DABCODC-5598) Air Products (PA) Catalyst-1 Iron acetyl acetonate dispersed inpolyol with acetyl Alfa Aesar (MA) acetonate (OH No. = 56) Catalyst-2Iron acetyl acetonate dispersed in diol with acetyl Alfa Aesar (MA)acetonate (OH No. = 1247)

An exemplary process for the production of the polyurethane foams usedin the examples is as follows. Part A (the polyol component, catalyst,and surfactant (foam stabilizer) and any other additives were mixed andplaced in a holding tank with agitation and under dry nitrogen. Thismixture was then pumped at a controlled flow rate to an Oakes-type highshear mixing head. Part B (the isocyanate component) was separatelypumped into the mixing head at a controlled flow rate relative to theflow rate of part A. Flow meters were used to measure and adjust theflow rates of the various raw material streams. Dry air was introducedinto the mixing head using a gas flow rate controller to adjust theairflow rate so as to create froth.

After mixing and mechanical frothing in the high shear mixer, the foamwas pumped through a flexible hose and out through a rigid nozzle. Thefoams were then cast onto a coated release paper that had been dried bypassing it through an infrared dryer just prior to the point where thefoam was introduced. The release paper was drawn through the machine atcontrolled speed.

The coated release paper was then passed through a curing section forabout 2 to about 8 minutes, consisting of exposure to heated platenskept at 120° C. to 190° C. by a series of thermocouples, controllers,and heating elements. A series of upper platens were kept at 220° C. Thecured product was then passed through a cooling section. The resultingsheet was die cut, the top surface was planarized, a groove pattern putinto the planarized surface, and the product mounted to a subpad asdescribed below to provide a finished polishing pad. A plurality ofspecimens was obtained for evaluating performance as achemical-mechanical polishing pad.

The samples were tested using the following methods and conditions.

Storage modulus was determined as described in U.S. Pat. No. 7,217,179using a strip having a width of 3 mm, a thickness of 1.5 mm and a lengthof 19 mm cut from a cured polyurethane sheet. The strip was measured ina DMA operating in tensile mode a frequency of 1.6 Hz, 0.5 N staticforce, a dynamic bias of 0.05%, and an initial load of 50 g. The samplewas equilibrated at −20° C. for 10 minutes and then ramped at a rate of5° C. per min to 120° C. using a commercially available dynamicviscoelasticity measuring instrument.

Energy loss factor (KEL), E′ ratio, and tan δ were determined by ASTMD4092-90 (“Standard Terminology Relating to Dynamic MechanicalMeasurements of Plastics”), incorporated by reference in its entirety.Measurement conditions were as described above.

Unless otherwise indicated, the weight of each of the specimens wasdetermined using an electronic force balance, and the density wascalculated using the formula:

Density (kg/m³)=[Weight(kg) of Specimen]/[Volume (m³) of Specimen].

Cell size was determined by a scanning electron microscope (SEM).

The Surface Energy of the surfaces of the pad with a skin, as producedbefore being ground and after being ground, was determined using sessiledrop goniometry. This technique is a known method used to characterizesurface energy. Sessile drop contact angles of water and diiodomethanewere measured using image analysis (Tangent Method 1) with the KrussDSA-10 MK2 Drop Shape Analysis System. Droplets were delivered at acontrolled rate and volume, with specimens held in place on a vacuumstage. The two-component Fowkes Method was used to generate surfaceenergy values from the mean (n=10) contact angle data. Effort was madeto place the droplets between the surface features of the polishingpads, such as grooves or perforations, and drop size was reduced toavoid capillary interaction with the grooves. The data excludedmeasurements where droplet distortion was evident and the mean (left andright) contact angles exceeded +/−1 degree. The test liquids aredescribed in Table 2.

TABLE 2 Reference surface tension Reference (mN/m) Percent Test Liquid:Source Total Disperse Polar Disperse Polar Water* (1.5 μL) Gebhardt72.80 46.80 26.00 64.29% 35.71% Diiodomethane (1.0-1.5μL) Fowkes 50.8048.50 2.30 95.47% 4.53% *High purity reagent grade water (conforms toASTM D-1193, Type I)

The CMP polishing pads were tested for chemical mechanical polishing ofcopper using an IPEC 372M-165 polishing machine. The polishingcomposition was DANANO Cu390 (800 g slurry, 300 g. distilled water, 138g of H₂O₂).

Pads were analyzed for total number of defects using a 0.25 micrometeror 0.20 micrometer size cut-off, employing screen capture of the defectanalysis, in which color of spots in an image were used represent thesize and number of defects in a wafer using an AMAT/Orbot WS-736.

Example 1

A polyurethane layer was prepared by the above-described process usingthe formulation shown in Table 3.

TABLE 3 Ex. 1 Component Parts Part A PTMEG 60.60 MP Diol 13.70 Triol13.41 Surfactant 1.88 Catalyst-1 5.81 PTFE No. 2 4.61 Total, Part A100.01 OH # 284 Part B Isocyanate 94.46 Total parts

The materials produced in accordance with this formulation were rigid,microporous, high modulus polyurethanes. The Mc (molecular weightbetween crosslinks) of the foamed, cured polyurethanes was equal to4521.33 for Example 1.

To test the material for use in CMP polishing, copper planarization wasconducted using a polishing pad (Example P-1) made from the formulationof Example 1, which was then compared to a conventional IC 1000 CMP padmanufactured by Rohm and Haas. The IC 1000 CMP pad was tested with aSUBA IV subpad manufactured by Rohm and Haas (the “C-1” pad). In orderto retain consistency, the inventive polishing pad P-1 washand-laminated onto a SUBA IV subpad. The polishing pads made inaccordance with the invention, however, were only 19.5 inches indiameter versus 22.5 inches in diameter for the IC 1000 polishing pad,which matches the diameter of the platen of the polishing machine.Compensation for this discrepancy was achieved by shortening theoscillation of the arm of the polishing machine during polishing of thewafer to a narrower sweep. This was done for both the IC1000 CMP pad andthe exemplary CMP pad for consistency.

Removal rate (RR) and “within wafer nonuniformity” (WIWNU) were bothdetermined. While the pads were conditioning on the platen withdistilled water, the IC1000 CMP pad exhibited a smooth, well wet-outappearance. In comparison, inventive Pad P-1 exhibited a discontinuouswet-out that was believed to be due to the incorporation of the PTFEfiller.

Certain polishing parameters were tested in order to determine theireffect on the removal rate profile, including the back pressure behindthe wafer, A more uniform removal rate was achieved using a backpressure of 3 psi and a slurry flow rate of 200 mL/min slurry flow rate.

Polishing of wafers, also referred to as planarization, was evaluatedafter a standard pad conditioning cycle of 10 minutes followed byplanarization of 10 filler wafers (6 oxide fillers and 4 copperfillers), followed by a copper monitor wafer for removal rateevaluation. This was sequentially followed by two more copper fillerwafers and a second copper monitor wafer. For the inventive Pad P-1, asequentially third copper monitor wafer was polished. All CMP processconditions were based on the optimal conditions for the pad determinedas described above. The wafers were cleaned using a standard cleaningprocess to help obtain accurate defectivity measurements.

Copper monitor wafers were polished using the indicated pre-polishingsequence, and their removal rate profiles were measured. Screen captureof the defect analysis was obtained for the wafers polished by the P-1and C-1 pads. The results are shown in Table 4.

TABLE 4 CMP Total Defects Monitor Polishing Pre-Polishing Removal RateWIWNU 0.25 μm 0.20 μm Wafer No. Pad Sequence (Angstroms/min) (Percent)cutoff cutoff 1A Ex. C-1 10 fillers 9484 3.9% 4,110 30,987 2A (IC 1000)10 fillers 9350 4.7% 4,028 Wafer no. 1A 2 Cu fillers 1B Ex. P-1 10fillers 9342 4.4% 1,136 3,546 2B 10 fillers 9495 3.7% 787 2,608 Waferno. 1B 2 Cu filler 3B 10 fillers 9474 2.7% 761 2,855 Wafer no. 1B WaferNo. 2B

These experimental results show that for copper planarization, the IC1000 CMP pad provided a removal rate of about 9,400 Angstroms/min, aWIWNU of about 4%, and about 4,000 total defects (0.25 μm cutoff). Theinventive Pad P-1 showed a comparable removal rate (about 9,500Angstroms/min) and WIWNU (about 4%), with greatly reduced total defects(800-1,000). This is a 4-fold reduction over the IC 1000 pad polishedwafers. If the cutoff for the defect analysis is changed from 0.25micrometers to 0.20 micrometers (a more difficult test to pass), thedecrease in the number of defects for the inventive samples is even morestriking: about 31,000 total defects for the prior art top pad and about2,600 to 4,000 for the inventive pads. These results indicated that theexcellent polishing performance of the present CMP pads providedimproved performance compared to a CMP pad meeting industry standards.

In addition to the results shown in table 4, the polishing temperatureof the surface of the pad during polishing was measured using an IRthermal gauge. Comparative Pad C-1 had a temperature of 125° F. (52.7°C.), while the inventive pad P-1 had a lower temperature of 119° F.(48.3° C.). Another run using another sample of the comparative Pad C-1and a pad manufactured using the formulation in Table 3 had a surfacetemperature during polishing of 120° (48.9° C.) and 110° F. (43.3° C.)

To determine whether extended polishing would affect defectivity,removal rate, or uniformity, of the inventive pad, the previously testedPad P-1, made using the formulation of Example 1, were used tosequentially polish additional wafers as indicated in Table 5. Theprocedure was to sequentially polish an additional two oxide fillers,followed by an additional two copper fillers, and then a copper monitorwafer. This cycle was repeated four times. Thus, for example, for thelast Monitor Wafer 7, the Pad P-1, in addition to the sequentialpolishing in Table 4, had additionally polished the following sequenceof wafers: 2 oxide fillers, 2 copper fillers, monitor wafer no. 4, 2oxide fillers, 2 copper fillers, monitor wafer no. 5, 2 oxide fillers, 2copper fillers, monitor wafer no. 6, 2 oxide fillers, 2 copper fillers,and monitor wafer no. 7. Results are shown in Table 5 below.

TABLE 5 Monitor Supplemental Removal Rate Total Defects WaferPre-Polishing (Angstroms/ WIWNU 0.25 μm 0.20 μm No. Sequence min)(Percent) cutoff cutoff 4 2 Ox filler 9568 3.5% 1,074 4,114 2 Cu filler5 2 Ox filler 9609 3.8% 1,988 9,848 2 Cu filler 6 2 Ox filler 9553 3.1%585 2,454 2 Cu filler 7 2 Ox filler 9997 4.1% 541 2,291 2 Cu filler

The results in Table 5 show no apparent deterioration or other trends.Removal rate for Wafer 7 was slightly higher, about 10,000 Angstroms/minvs. an average of about 9,500 for the others. Also, total defects forone of the wafers (Wafer No. 5) was about 2,000, which is over two timesthat of the others, which likely may have been caused by the samplewafer rather than the polishing pad.

Example 2

Various formulations were prepared containing hydrophobic particles.FIG. 1 shows a scanning electron microscope (SEM) of a polyurethanematerial generally produced according to the examples described hereinwithout PTFE particulates and FIG. 2 shows a comparable formulation withPTFE particulates. It can be observed that the general effect of thePTFE particulates in the polyurethane foam is to produce smaller andmore uniform cells, based on the SEM image.

The skin surface of the polyurethane material of FIG. 2 was measuredusing the above-described Surface Energy Test. The results for contactangle (CA) and surface energy are shown for in Table 6.

TABLE 6 CA (deg) [Tan Method 1] Surface Energy (mN/m) Waterdiiodomethane [Fowkes Method] % Component Sample mean (±) mean (±) Total(±) Disperse (±) Polar (±) Disperse Polar Skin surface 93.3 2.13 72.21.92 22.26 2.20 19.21 1.30 3.06 0.90 86.3% 13.7%

Thus, it is believed that the presence of the hydrophobic particleslowers the surface energy of the polyurethane material. In forming theCMP polishing pad, the skin surface as produced can be ground, which canmodify the measured surface energy of the polyurethane.

Examples 3-6

These examples illustrate adjustment of the modulus properties of apolyurethane material for use in a CMP polishing, by varying theconcentration of the various components of the reaction mixture forforming the polyurethane material. Top pads based on the twoformulations shown in Table 7 were prepared.

TABLE 7 Example 3 Example 4 Material Parts Parts Part A PTMEG polyol66.41 63.41 MP Diol 7.89 10.89 Triol 13.41 13.41 Surfactant 3.76 3.76Catalyst-2* 5.81 5.81 PTFE No. 2 4.61 4.61 Total, Part A 101.89 101.89OH # 280 315 Part B Isocyanate 93.01 106.65 *Diluted in polyol

The microporous top pads produced in accordance with Examples 3 wassimilar to the formulation of Example 1 above. Example 4 was aformulation for a more firm material. The firmer material of Example 4contained a relatively higher proportion of low molecular weight chainextender, and the softer material of Example 3 contained a comparativelylower proportion of low molecular weight chain extender.

The various materials were then subjected to dynamic mechanicalanalysis. Since chemical mechanical polishing is usually not conductedat below room temperature, the results for 20 and 50° C. are presentedbelow for Examples 3-4 and also a comparative polishing pad, C-2 (IC1000 top pad from Rohm & Haas). Results are shown in Table 8.

TABLE 8 Property Ex. 3 Ex. 4 Ex. C-2A C-2B E′ at 20° C. (MPa) 420 529363  178  E′ at 40° C. (MPa) 349 450 286* 138* E′ at 50° C. (MPa) 303396 250* 120* Tan δ at 20° C. 0.042 0.036    0.071    0.075 Tan δ at 40°C. 0.048 0.039    0.073    0.080 Tan δ at 50° C. 0.061 0.050    0.074   0.086 KEL at 20° C. (1/Pa) 99 68 195* 419* KEL at 40° C. (1/Pa 136 86254* 574* KEL (1/Pa) at 50° C. 201 126 295* 713* KEL ratio 50° C./20° C.2.0 1.8   1.5   1.7 Tan δ ratio 50° C./20° C. 1.47 1.38   1.04   1.15 E′ratio 50° C./20° C. 0.72 0.75   0.68   0.69 *Discrepancy betweenmeasurements for Exs. C-2A and C-2B possibly attributable toperforations in the samples.

Thus, based on the results in Table 8, it was found that a polishing padsimultaneously having comparatively higher storage modulus and lower tanδ and/or lower KEL was produced, in which the KEL ratio and/or tan δratio demonstrated relatively low physical property changes over therelevant temperature range of up to 50° C. These properties were foundto be associated with advantageous polishing efficiency at a lowerdefect level, as well as lower temperatures produced during polishing. Agraph of tan delta vs. temperature is shown in FIG. 3 for inventive Ex.3 and comparative Ex. C-2A. This graph shows that the tan delta of theinventive compositions is less than 0.070 over a range of 20° C. to 50°C.

To further test the relationship between modulus, tan δ, and otherparameters, a still lower and a still higher modulus top pad was formedfrom the formulation shown in Table 9.

TABLE 9 Example 5 Example 6 Material Parts Parts Part A PTMEG polyol73.3 58.41 MP Diol 1.00 15.89 Triol 13.41 13.41 Surfactant 3.76 3.76Catalyst-2* 5.81 5.81 PTFE No. 2 4.61 4.61 Total, Part A 101.89 101.89OH # 199 373 Part B Isocyanate 67.48 124.12 *Diluted in polyol

In particular, the top pad produced in accordance with Example 5 was ofa lower modulus (softer) polyurethanes, and the top pad produced inaccordance with Example 6 was of a higher modulus (firmer)polyurethanes. The material of these top pads were then subjected todynamic mechanical analysis, as before. In addition, further samples ofthe formulations of Examples 3-4 were tested. Multiple samples (A, B,etc.) of each pad material were tested and the results are shown inTable 10.

TABLE 10 Property Ex. 5A Ex. 5B Ex. 5C Ex. 3A Ex. 3B Ex. 3C Ex. 4A Ex.4B Ex. 4C Ex. 6A Ex. 6B Density, pcf 50.1 51 69.3 46.5 51.2 69.8 46 6951 45.2 52 (kg/m³) (802) (817) (1110) (745) (820) (1118) (737) (1105)(817) (724) (833) E′ at 20° C. 188 133 344 428 517 905 527 1020 676 637779 (MPa) E′ at 50° C. 82.8 55.0 153 300 379 636 394 787 515 540 635(MPa) Tan δ at 20° C. 0.109 0.106 0.120 0.0453 0.0457 0.0503 0.04070.0406 0.0402 0.040 0.0321 Tan δ at 50° C. 0.157 0.171 0.159 0.06540.0574 0.0626 0.0533 0.0500 0.0503 0.0487 0.0361 KEL at 20° C. 572 786344 106 88.2 55.4 77.1 39.7 59.4 62.8 41.1 (1/Pa) KEL (1/Pa) at 18503030 1010 217 151 98.0 135 63.4 97.4 90.1 56.7 50° C. KEL ratio 3.233.85 2.94 2.05 1.71 1.77 1.75 1.597 1.60 1.44 1.38 50° C./20° C.

Based on the results in Table 10, it was found that reproducible resultscould be obtained for a polishing pad having an improved relationship ofa comparatively higher storage modulus and relatively lower tan δ and/orlower KEL. A softer pad, however, tends to exhibit a higher tan δ, and afirmer pad tends to exhibit a relatively lower tan δ. Finally, asdesired, the KEL ratio and/or tan δ ratio demonstrated relatively lowphysical property changes over the relevant temperature range of up to50° C. The desired firmness of the top pad for a particular application,however, may depend on the specific material being polished and thedesired polishing rates and defect levels. An important advantage ofthis invention is the ability to produce a range of densities and thus arange of moduli with the same formulation. Higher densities for a givenformulation will produce higher modulus along with fewer cells. Thus,the mechanical and polishing performance properties of the pad can beadjusted by independently controlling the composition and the density.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. The endpointsof all ranges reciting the same characteristic or referring to aquantity of the same component are independently combinable andinclusive of the recited endpoint, as well as throughout the range. Theterms “first,” “second,” and the like do not denote any order, quantity,or importance, but rather are used to distinguish one element fromanother. All references are incorporated herein by reference.

The present examples and embodiments are to be considered asillustrative and not restrictive and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1-15. (canceled)
 16. A polishing pad, comprising a polyurethane layer,wherein the polyurethane layer comprises a polyurethane foam, whereinthe polyurethane foam has a density of about 640 to about 1200 kg/m³,and a plurality of cells having an average diameter of 20 to 200micrometers, and the polyurethane layer has: a KEL of about 1 to about500 1/Pa at 50° C., a storage modulus of greater than 100 MPa in therange of 20° C. to 50° C., a tan δ of less than 0.070 in the range of20° C. to 50° C., and a ratio of tan δ at 50° C.:tan δ at 20° C. of 1.2to 3.0; wherein the polyurethane layer functions as a polishing layer ofthe polishing pad, which polishing pad is capable of use for planarizinga work piece in conjunction with a chemical-mechanical polishingapparatus.
 17. The polishing pad of claim 16, wherein the surface energyof the polyurethane layer as produced is 18 to 30 mN/m.
 18. Thepolishing pad of claim 16, wherein the polyurethane is produced in thepresence of a ferric acetyl acetonate catalyst. 19-20. (canceled) 21.The polishing pad of claim 16, wherein the pad exhibits a defect rate ofless than 3500 based on a 0.25 μm cutoff.
 22. The polishing pad of claim16, wherein the pad exhibits a defect rate of less than 20000 at a 0.20μm cutoff.
 23. The polishing pad of claim 16, wherein the polishingsurface has been ground to remove the skin from the surface of apolishing pad.
 24. The polishing pad of claim 16, wherein the polishingsurface of the polishing layer further comprises grooves.
 25. Thepolishing pad of claim 16, wherein the polishing pad is a composite padcomprising the polishing layer disposed on a substrate layer of anotherpolyurethane foam or elastomeric material that is integrally bonded tothe polishing layer.
 26. The polishing pad of claim 16, wherein thepolyurethane foam has been made by a process comprising mechanicalfrothing.
 27. A method of planarizing a surface of a work piece,comprising applying a particulate media against said surface, androtating, relative to said surface, the polishing pad of claim
 16. 28.The method of claim 27, wherein polishing is by means of a polishingmachine employing a down force of 35 to 700 g/cm², a platen speed of 25to 400 rpm, a carrier speed of 25 to 400 rpm, and a media flow of 20 to500 mL/min.
 29. The polishing pad of claim 16, wherein the polyurethanefoam is the reaction product of an isocyanate-containing component; anactive hydrogen-containing component reactive with theisocyanate-containing component, and comprising a polyether polyol ofthe formula R[(OC_(n)H_(2n))_(z)OH]_(a), wherein R is hydrogen or apolyvalent hydrocarbon radical; a is 2-8 and equal to the valence of R;n in each occurrence is an integer from 2-4; and z in each occurrence is2 to about 200; a silicone surfactant, and a catalyst for curing of thefoam.
 30. The polishing pad of claim 29, wherein theisocyanate-containing component comprises a prepolymer that comprisesthe reaction product of a diisocyanate compound with glycol.
 31. Thepolishing pad of claim 29, wherein the polyether polyol ispolytetramethylene ether glycol.
 32. The polishing pad of claim 29,wherein the active hydrogen-containing component further comprises adiol chain extender.
 33. The polishing pad of claim 29, wherein thesurfactant is a nonhydrolyzable silicone glycol copolymer.
 34. Thepolishing pad of claim 16, wherein the polyurethane foam has a densityof 640 to about 960 kg/m³.
 35. The polishing pad of claim 16, whereinthe polyurethane layer has a thickness of 0.5 to 5.0 mm.
 36. Thepolishing pad of claim 16, wherein the polishing layer is adapted forpolishing a microelectronic work piece of a work piece comprising asemiconductor base material.
 37. The polishing pad of claim 16, whereinthe polyurethane foam further comprises particles of a hydrophobicpolymer having a critical surface energy of less than 35 mN/m and havinga median particle size of 3 to 100 micrometers.